In microwave or high frequency devices in which high frequency energy is coupled from a resonant cavity or into such a cavity, it is often a requirement that the degree of coupling into or out of the cavity is adjustable by rotating a coupling loop or other coupling means located within the cavity. This adjustment is normally carried out manually. In a known adjustment arrangement, a coupling loop to be rotated is fixed to a ceramic disc having a raised metal rim. The disc is located in an aperture in the cavity wall and is rotatable relative to the wall. An endless drive belt passes over the metal rim to a knob rotatably secured to the cavity wall and positioned to be accessible to an operator. When the operator turns the knob, the drive belt transmits this movement to the rotatable disc and hence to the coupling loop. To allow rotation of the disc, there is a gap between its metal rim and the surrounding metal cavity wall. Metal spring fingers are located around the edge of the metal rim and press against the wall of the aperture in the cavity wall to prevent leakage of high frequency radiation through the gap. Such an arrangement can be used to provide adjustment of a coupling loop in a single cavity or by a suitable mechanical connection to loops in different adjacent resonant cavities. If independent control of the orientations of coupling loops in adjacent cavities is required, then two sets of adjusting knobs and drive belts are provided.
The present invention seeks to provide an improved actuator for providing rotation of coupling means in a high frequency resonant cavity.